Estimation of vehicular emission coefficients for countries without emissions inventories: A case study of Kenya

摘要

The recognition of the contribution of vehicular emissions to atmospheric pollution has led to much research and inventory build up particularly in the industrialised countries. Consequently, emissions data for use in planning analysis is readily available in there, but in the vast majority of developing countries, Kenya included, and this is not the case. It is generally accepted that due to a variety of factors, the emissions rates for vehicle fleets in developing countries are higher than those of similar vehicles in developed countries. These factors include poorer maintenance conditions, the longer service life and the amount of load the vehicles have to carry. However, there is hardly any prior research aimed at trying to cost effectively estimate the actual emission parameters in these countries. This paper proposes a new approach that has been developed and applied to estimate emission coefficients for CO, HC and NOx in Kenya. The main premise of this approach is to acceptably estimate adjustment factors with which emissions coefficients from industrialised countries can be modified to suit the vehicle fleet in a particular developing country. Descriptive data which included age, make, country of manufacture and the presence or absence of emissions control equipment was used to classify vehicles into various technology layers. Each layer was associated with a specific emissions rate, which was then modified by maintenance, age and mileage and loading factors to estimate the Kenyan situation. The maximum values of the adjustment factors were derived based on literature, theoretical framework and on empirical data obtained using a floating vehicle in Germany. These values represented the worst case scenario and two other scenarios were built with lower values. The Kenyan situation was thought to be best described by the middle scenario. Emissions coefficients for Kenyan vehicles were estimated to be up to two to three times higher than typical values in industrialised countries (for Germany up to two times). It was not possible to directly validate these emission values but as a good indicator, comparison of the actual fuel consumption data was done between vehicles in Kenya and those in Germany under similar driving conditions. It was found that the consumption rates in Kenya were also significantly higher (up to 65% higher), thus lending credence to the estimated factors. It was therefore concluded that, whereas the proposed method is not expected to estimate emission rates with a high accuracy, it could nevertheless give acceptable results for use in countries devoid of emission inventories.